1. ECE 6610 Sandeep Kakumanu GNAN research Lab
Network Simulator - ns2
ECE 6610
Sandeep Kakumanu
GNAN research Lab

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Assignment 1 has been posted.

3. Outline Discrete event Simulations ns-2 architecture Working with Tcl
Working with C++
Important files
Trace analysis
Miscellaneous
Assignment 1 overview

4. Classification of simulation paradigms
Computer simulation
Discrete models
Continuous time models
event driven
time-stepped

5. Discrete event simulations:
As-fast-as-possible execution of simulation as opposed to scaled real-time simulation.
Event based scheduling.
A single queue of events.
Each event has a time stamp. Chronological execution of events.
An event might create more events. These new events are inserted into the queue.

6. Ns-2: Introduction NS-2: network simulator version 2
Discrete event simulator
Packet level simulation
Features
Open source
Scheduling, routing and congestion control
Wired networks: P2P links, LAN
Wireless networks: terrestrial (ad-hoc, cellular; GPRS, UMTS, WLAN, Bluetooth), satellite
Emulation and trace

7. Ns-2 Paradigm Object-oriented programming Protocol layering
Modularity and extensibility
Large scale simulation
Maintenance and reusability
Split-language programming
Scripting language (Tcl)
System programming language (C++)

8. Ns-2: Split Languages Tcl scripts (Tcl/OTcl) Interpreted (interactive)
Setup and configuration
C codes (C/C++)
Compiled (efficient)
Algorithms and protocols
TclCL (OTcl/C++)
Link Tcl/OTcl scripts and C/C++ codes
Provide a layer of C++ glue over OTcl

9. OTcl/C++ split objects
NS-2: Split Objects
OTcl/C++ split objects
Pure OTcl
objects
Pure C++
objects
TclCL linkage
OTcl
C++
NS-2

10. NS-2: Directory Structure
ns-allinone
...
Tcl8
TK8
OTcl
TclCL
ns-2
nam-1
tcl
...
C++ code ex
test
lib
mcast
...
examples
validation tests
OTcl code

11. Structure of a wired node

12. Structure of a wired simplex link

13. A wired LAN

14. A wireless node

15. Setting up ns-2
Requirements: Linux box with at least 500 MB free space.
Download the latest ns-allinone-2.33.tar.gz from the ns-2 website (google ns-2).
Untar the archive:
> tar –xvfz ns-allinone-2.33.tar.gz
Install:
> cd ns-allinone-2.33
> ./install
Setup the environment variables in the bash or csh script.
Close xterm and open again.
ns-2 should work now.

16. Setting the environment variables
Bash:
$ vi .bashrc
export PATH=$PATH:/path_to_ns-allinone-2.33/bin:/path_to_ns- allinone-etc/
export LD_LIBRARY_PATH=$PATH:/path_to_ns-allinone…etc/
export TCL_LIBRARY=$PATH:/path_to_ns-allinone…etc/
Csh:
> vi .cshrc
setenv PATH /path_to_ns-allinone-2.33/bin:/path_to_ns-allinone- etc/:$PATH

17. Working with tcl Tcl is the front-end in ns-2.
Define node configurations, node topology, agents etc.
Agents can be UDP/TCP, CBR/FTP/VBR/Webtraffic/...
For wired nodes: setup links, define link delays, link errors, define LAN configurations, buffer sizes...
For wireless nodes: node positions, node mobility, chose from different MAC, routing protocols.
Simple procedures for printing aggregated results like total throughput, total simulation time etc.

18. Working with tcl (cont'd)
A command consists of words
cmdName arg1 arg2 …
cmdName: core command or procedure
set, puts, expr, open, if, for, …
All words are considered as strings
White space (space/tab) separates arguments
Newline or semicolon (;) terminates a command
Command evaluation: parsing and execution
The interpreter does “substitution” and “grouping” (parsing) before running a command
Every command returns a result string after execution

19. Basic Tcl commands:
puts - tcl equivalent of printf
Ex – puts $a; #will print the value of a
set – set value to variable
Ex – set a 3; #set value of a=3
expr – evaluate a mathematical expression
Ex – expr $a+2 ; #add 2 to a.
Complex groupings:
set rate [expr 5*$a]; #compute a*5 and set to rate

20. Tcl: procedures Procedures are like functions in C.
Variables defined outside a procedure are invisible inside it. Global variables are visible everywhere.
Variable length of arguments using args.
Examples
proc add args {
set s 0
foreach i $args {incr s $i}
return $s }
proc inc {var {dv 1}} {
set a [expr $var+$dv]
return $a }

21. Tcl Core commands Control flow if, switch, while, for, foreach
File access
open, close, flush, puts, gets
String manipulation
glob-style and regular expression
List manipulation
llength, lindex, linsert, lreplace
lappend

22. A simple tcl script set ns [new Simulator]
set nf [open out.tr w];$ns trace-all $nf
for {set i 0} {$i<2} {incr i} { ;# create the nodes
set n($i) [$ns node]}
$ns duplex-link $n(0) $n(1) 1Mb 10ms DropTail
set udp(0) [new Agent/UDP] # Create a UDP agent
$ns attach-agent $n(0) $udp(0) set null0 [new Agent/LossMonitor] $ns attach-agent $n(1) $null0 set cbr(0) [new Application/Traffic/CBR] $cbr(0) set packetSize_500 $cbr(0) set rate_ 100kb $cbr(0) attach-agent $udp(0) $ns connect $udp(0) $null0 $ns at 0.0 "$cbr(0) start" $ns at 10.0 "$cbr(0) stop"
proc finish {} {
global ns nf
$ns flush-trace; close $nf }
$ns at 10.0 "finish"
$ns run

23. Working with C++ All protocols are written in C++.
Everything is an object. Otcl will attach the necessary C++ objects.
All objects are inherited from tclclass.
Every object has atleast one header (.h) file and one .cc file.
Different objects talk to each other using packets.
Every object has a recv() function which receives a packet, and has pointers to all the other attached objects known as targets (uptarget_, downtarget_ etc).

24. Packet Packets are events Can be scheduled to “arrive”
Packets contain header section and data
Header section is a cascade of all in-use headers
Each packet contains a common header
packet size (used to compute transmission time)
packet type
timestamp, uid, …
All in-use headers are included when simulation starts
Change packet size to reflect header cascading

25. Important files packet.h – defines all the headers for packets.
scheduler.h,.cc – the C++ scheduler class.
agent.h,.cc – the base class for all agents.
tcp.h,.cc – TCP, udp.h,.cc – UDP, cbr_traffic.cc – cbr traffic, mac-802_11.h,.cc – MAC.
tcl/lib/ns-defaults.tcl – All the default parameters for configurations of the various protocols.
tcl/lib/ns-lib.tcl – Otcl script connecting the various layers of the network stack in a single node.

26. Modifying C++ files Modify existing C++ files.
C++ files are inside /path/ns-allinone-2.33/ns-2.33 directory.
The directory also has a Makefile.
When you edit only a .cc file:
$ make
When you edit a .h file:
$ make clean

27. Traces Ns-2 simulations provide a number of traces.
A trace file is used for post-processing of the simulation and find out what events happened at different times of the simulation.
Traces for wired and wireless simulations have different format.
Traces are text files.
Trace formats at: 2_Trace_Formats
Different ways to parse the traces – C, awk, perl... Use anyone in which you are comfortable.

28. Sample trace
cbr cbr cbr cbr cbr cbr r cbr cbr cbr cbr cbr r cbr cbr cbr cbr

29. Miscellaneous utlities
nam – Network animator: Used to animate the network events after the simulation has finished. nam will parse a name trace and show the animation.
cbrgen – create traffic patterns.
setdest – generate wireless topologies and set up mobility patterns using random waypoint model.

30. More help Marc Greis tutorial (Chapters I-VI & VIII-XI). ns-2 manual.
ns-2 mailing list.
T-square wiki.

31. Puzzle Are there two dogs in world with the same number of hairs ?
(Make reasonable assumptions)